The forming of composite articles typically requires heating a preform while applying compressive force during consolidation of the preform. When heating the preform, it is typically desirable to maintain the preform at an elevated temperature and within a relatively narrow temperature range corresponding to the material system or resin composition of the preform so that the desired mechanical properties will be achieved in the final article. When forming a thermoplastic article, it may be necessary to heat the preform above the melting temperature of the thermoplastic resin such that the resin may flow throughout the preform during consolidation.
To achieve the desired mechanical properties in the thermoplastic article, it may also be necessary to thermally cycle the preform by reducing the temperature of the preform from the melting temperature to a second, lower temperature and maintain the preform at the second temperature for a predetermined time period. By maintaining the preform at the second temperature for the predetermined time period, the desired level of crystallinity may be achieved in the thermoplastic article which may affect the mechanical properties of the final article. The mechanical properties of the final thermoplastic article may also be affected by the rate at which the preform is heated and/or cooled during thermal cycling.
Conventional techniques for forming composite articles include the use of an autoclave and conventional tooling for consolidating the preform and forming the preform in the desired shape. Unfortunately, autoclaves and tooling typically have relatively large thermal masses which results in a significant amount of time for initially heating the preform to the melting point. In addition, the relatively large thermal mass of an autoclave and tooling results in a significant amount of time for the article to cool during thermal cycling. Furthermore, the relatively large thermal mass of the autoclave and tooling reduces the ability to maintain the article at the desired temperatures for the specified time periods to achieve optimal mechanical properties in the final article.
Additional drawbacks associated with the use of autoclaves and conventional tooling include difficulty in applying heat to the article in a uniformly-distributed manner due to the relatively large thermal mass of the autoclave and tooling. Furthermore, the large thermal mass of the autoclave and tooling results in relatively long time periods to allow the article to cool to a temperature safe for handling. In addition, autoclaves consume relatively large amounts of electrical power during the initial heating of the autoclave interior and the tooling.
As can be seen, there exists a need in the art for a system and method for heating a preform that provides a high level of controllability of the temperature to which the preform is heated. In addition, there exists a need in the art for a system and method that facilitates heating and cooling a preform in a relatively short period of time and in a controlled manner such that the mechanical properties of the final article may be optimized. Furthermore, there exists a need in the art for a system and method for heating a preform that results in the uniform distribution of heat throughout the preform. Preferably, such a system and method may be operated in an energy-efficient and cost-effective manner.